I wouldn't say that any rebreather is trying to kill you, but you must admit that some of the failure modes involves a loss of sentience...
What is "recreational" rebreather, and any recommendations?
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I wouldn't say that any rebreather is trying to kill you, but you must admit that some of the failure modes involves a loss of sentience...
silent running
Contributor
Oxygen toxicity and PO2 tolerance is highly variable person to person. The CNS clock and OTU measurements are very crude and not scientifically validated, they are guidelines at best. I dived 20 days straight, 1.3 SP 4-6 hours a day and never even got the dry cough some people experience with long, high PO2 exposures on single dives.
A course will give you some understanding of theory and best practices, not much else. Unfortunately the effects on the human body of constant PO2 diving, and diving with helium based mixtures are not fully understood. All CCR divers are practicing hyperbaric medicine on themselves. Continuing education for CCR divers is mandatory, IMHO...
silent running
Contributor
Sure, if you don’t do what you’re supposed to, like verifying your gas mixtures, checking cells for current limiting at 1.6 or above in the water and packing your scrubber properly. If you do those things I see no possibility of losing consciousness.
Overbreathing the unit due to unexpected work (like your downcurrent story) . Mushroom valve damage or debris.
Look, don't get me wrong. I love my rebreather. And good attention to detail can pick up most failure modes before they become lehal. But I wouldn't go so far as to imply that any human pilot can guarantee that no such circumstances will ever exist because they always do everything right.
silent running
Contributor
As a guy who used to ride motorcycles and was injured badly riding them, I think CCRs are way safer. It is interesting to note that most of the motorcyclists I have met never talk about the dangers of motorcycles. I would say that risks associated with CCRs and the environmental variables encountered in their use are much more limited than those when operating a motorcycle in traffic, with weather and road conditions as well.
How common is over breathing a properly packed scrubber? How often do flapper valves fail? I’ve been diving RBs a long time and never had either of those 2 things happen. I breathe/pressure check my flappers every time I assemble my CCR, takes 30 seconds. I also inhale and exhale rapidly during every dive to listen for the heathy popping sound they make when working correctly. And since you mention it, my down current experience occurred when my radial scrubber was in its last hour before changing. I’ve had a giant tear in my exhale CL and had it fill half way up during a 3hr dive. I didn’t even notice until I got out of the water, and none of it made it into the scrubber, thanks to the OTS CL design...
silent running
Contributor
To the OP, regarding recommendations for a CCR, I love my Prism 1 and they can be found very cheap. It’s by far the simplest electronically controlled CCR, encourages maximum diver involvement for an ECCR and has some excellently designed safety features, like that it can be dived with no power or electronics as the secondary PO2 gage is driven directly by the high current sensors.
All that being said, if I were getting certified today, I would probably go with a manually controlled CCR with an adjustable O2 valve like the Pelagian or the Fathom. They are very easy to use, simple, reliable and give you maximum flexibility in terms of types of diving. I would not want an ECCR if I were planning on doing anything with frequent depth changes, like underwater photography or more advanced diving in overhead environments like wrecks or caves.
All that being said, if I were getting certified today, I would probably go with a manually controlled CCR with an adjustable O2 valve like the Pelagian or the Fathom. They are very easy to use, simple, reliable and give you maximum flexibility in terms of types of diving. I would not want an ECCR if I were planning on doing anything with frequent depth changes, like underwater photography or more advanced diving in overhead environments like wrecks or caves.
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Tell that to the widow who lost her husband in HI last year
Or the parents of Rob Stewart
There are hundred of "loss of consciousness" CCR victims - and the causes aren't even on your mini list there. You are simply wrong.
silent running
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If my understanding is correct:
Rob Stewart was not diving anything like recreational profiles and apparently diving trimix with very few hours.
Brian Bugge was on a tmix training dive, additionally task loaded with a camera, did not have his electronics in dive mode and his O2 was off.
Not paying attention to your PO2 and whether or not you have your gas turned on is at the top of the list of things you are supposed to do. Training involves instilling proper practices and the requisite hours to build muscle memory for the physical tasks of CCR diving. I would never take a camera on a training dive, nor should any instructor allow a student to do so. I’ve jumped in the water with my gas off several times, and each time I noticed that I had done so, either because I could not get a breath off my inhale/dil CL or because my PO2 was not rising, and quickly opened the valves. IMHO, all CCRs should have valves down and easily reachable for just this reason. I was also trained to watch my Smithers color coded HUD and check my secondary to make sure my PO2 rises during descent, and to watch for the PO2 to drop on ascent. This was second nature because I was made to manually add O2 for the first 4 days of training and only allowed to turn on the electronics at the end of the course. Good training emphasizes diver awareness of the proper functioning and principles of a CCR, and to cross check this multiple ways during the dive, like listening for the solenoid and making sure the sensors react.
Is there a way to lose consciousness that does not require multiple, crucial mistakes on the part of a CCR diver?
I can't give you a number, but the point is that there are two ways of developing hypercapnea - scrubber bypass (e.g. an improperly packed scrubber), and CO2 overproduction (e.g. suddenly having to do a lot more work, like someone caught in a downcurrent, as you mentioned upthread). If the problem is overbreathing, that means that the scrubber itself was not the problem. The fact that you personally were able to avoid hypercapnea with sudden unanticipated extra exertion in that specific instance doesn't mean that overbreathing isn't a thing.
No idea, I was just thinking of that duckweed report that I read a while ago (foreign object got into the downstream valve, keeping it from sealing).
Well, there you go. Survivor bias.
In my small sample of people that I actually know, I have lost two well trained and experienced friends who were diving CCR. In both cases, it was never clear what the exact sequence of events was, but people who have had CO2 hits describe being barely able to bail out (the argument for BOVs).
Look, you have a lot more experience than I do. And I'm not one of those people who know nothing about CCRs but go on and on about how they involve completely unacceptable risk. I also understand that CCR removes some OC risks. And I love my JJ.
I just don't think that you should imply that it is impossible to have a CCR catastrophe if you always do the right thing, because the point is that human beings - even really skilled and well trained ones - occasionally don't do the right thing. That's why I have been pushing to change rebreather culture about checklists. The point is that even the most well trained and experienced diver is running on human brain software, and we all can have occasional failures of that system. If you are sick, hungry, angry, dealing with an emergency, or whatever.
So yes, if you never make a mistake, it's pretty unlikely that your rebreather itself will do you in. I just don't think that your position is a good one to promote to OC divers considering making the switch to CCR.
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